As an ultraviolet laser device of the type described above that includes a laser beam output unit and a wavelength conversion unit, for example, a laser device that is used in an exposure device, an inspection device, a therapy device or the like is per se known. Generally, this type of laser device is built so as to amplify laser light on an infra-red wavelength emitted from a laser light source such as a DFB semiconductor laser or the like with an optical fiber amplifier, and so as to convert the wavelength of the amplified infrared light with an optical wavelength conversion element that is fitted to a wavelength conversion unit, thus outputting laser light on an ultraviolet wavelength. Due to the historical circumstances of optical fiber development, an erbium (Er) doped optical fiber amplifier (usually abbreviated as an “EDFA”) that amplifies infra-red laser light on the 1.55 μm wavelength band is widely used for the optical fiber amplifier.
On the other hand, in devices of various types that use ultraviolet laser devices as light sources, while forming and observing minute structure become easier the shorter is the wavelength of the ultraviolet light to be outputted, the optical materials that are transparent in the ultraviolet region of 235 nm and below is limited. The oscillation wavelength of an ArF excimer laser is 193 nm, and this is already implemented in practice as an ultraviolet laser device. Accordingly, a wavelength conversion unit of an ultraviolet laser device has been built so as to wavelength convert an infra-red laser beam outputted from a laser light unit into ultraviolet laser light on the wavelength band of 190-200 nm, this being outputted (refer to Patent Documents #1 and #2). With this type of structure, an ultraviolet laser device that is compact and entirely solid-state, and that is easy to handle and operate, is implemented that outputs ultraviolet light on the wavelength band described above.